As described in my German patent No. 2,847,927, a chuck has a chuck body centered on an axis, carried on a spindle of a hammer drill, and formed with several angularly equispaced guide passages extending at an acute angle to the chuck axis and receiving respective axially slidable jaws. An adjustment sleeve carried on the chuck body centered on the chuck axis and rotatable thereabout on this body is fixed to a ratchet ring having an inner surface formed with a screwthread that meshes with outwardly directed complementary teeth on the jaws. Thus rotation of the sleeve in a tightening direction moves the jaws along their guides from a back position in which they are radially relatively far apart to a front position in which they are relatively closely spaced and opposite rotation moves the jaws further apart.
In order to prevent such a chuck from loosening, the chuck body is formed with a guide passage that slidably receives a detent pin movable secantally relative to the chuck axis and urged outward by a spring so that its outer tip engages between radially inwardly directed teeth formed in this adjustment sleeve. A lockout ring can be turned on the chuck body about the chuck axis and has a lower edge just projecting to level with this detent. This ring has an inner surface engaging radially inward against the detent and formed with a pocket so that this ring can be rotated between an adjustment or holdback position in which its surface bears against the detent and holds the detent tip clear of the teeth and a ratcheting position in which the pocket is aligned with the detent so its spring can urge it outward along its secantal axis to engage its tip between the teeth.
Thus when the lockout ring is in the ratcheting position, rotation of the ratchet ring in the tightening direction will engage the forwardly directed flanks of the teeth against the tip of the detent and will push it along its axis back into the chuck body, allowing such rotation of the ratchet ring in the tightening direction. Opposite rotation will be impeded as the rear flanks will engage flatly against the rear side of the tip, in a direction perpendicular to the detent axis and to the force of its spring, so that the detent pin will merely be wedged sideways in its guide passage. Thus when aligned with the respective pocket of the lockout ring this detent pin allows the chuck to be tightened but prevents it from loosening.
Such an arrangement does indeed effectively prevent the chuck from loosening once it has been tightened on a tool or workpiece. In addition it allows overtightening after the workpiece or tool has been fitted, to compensate for any loosening that might occur.
The principal disadvantage of such a system is that it allows the chuck to be tightened enough to damage the tool or workpiece. When used in a hammer drill this arrangement allows the user to tighten down the chuck enough to cause the jaws to bite into the tool, whereas the chuck need only be tight enough to provide good transmission of torque, while permitting some relative axial displacement between the jaws and the bit.